Step 1

Preheat oven to 350°F.

Step 2

In a large bowl, whisk melted butter and 2/3 cup brown sugar until well combined, about 1 full minute. Add eggs, mashed banana and vanilla, whisking until combined.

Step 3

In a separate bowl, combine the flour, baking soda, salt, and cinnamon. Add dry ingredients to the wet ingredients and use a rubber spatula to lightly stir the batter until almost combined. Add 1/2 cup walnuts and stir until no streaks of flour remain. Be careful not to over-mix.

Step 4

Grease 15 standard-sized muffin cups and divide the batter evenly among the cups. Sprinkle the top of the each cup with brown sugar and chopped walnuts (topping). Bake for 14-17 minutes, until a toothpick inserted into the center comes out clean. Place the pan on a wire rack to cool.